Intertropical Zone Research Articles

Chromosome-level genome assembly of Fistularia commersonii (Syngnathiformes, Fistulariidae)

The bluespotted cornetfish (Fistularia commersonii), a Lessepsian sprinter species, is distributed in the inter-tropical zone across the entire Indo-Pacific, ranging from the Tropical Eastern Pacific to the Red Sea. In this study, we achieve assembly of a chromosome-level genome for F. commersonii by harnessing the precision of PacBio HiFi sequencing in conjunction with the sophistication of Hi-C sequencing technologies. The assembly yields a size of 638.75 Mb, achieving a distribution rate of 99.35% across 36 chromosomes. Notably, the contig N50 value stands at 15.67 Mb, while the scaffold N50 value reaches an impressive 18.69 Mb. BUSCO analysis demonstrates a genome completeness of 96.9% for F. commersonii. Repetitive elements constitute approximately 29.61% of the genome’s size. A total of 20,961 protein-coding genes are predicted, with 95.97% of them having functional annotations. This high-quality assembly provides crucial resources for future studies on the invasion mechanisms of F. commersonii, as well as for comparative genomics research on seahorses and pipefish.

Geotechnical mapping of lateritic gravels for efficient road construction in Cameroon’s intertropical zone

The study shows that the effective and timely construction of roads in the intertropical zone is hindered by the lack of geospatial data on the distribution of lateritic gravels (LG). This study uses a multicriteria geographic information system (GIS) mapping of elevations, relief curvature, slope classes, and rock types to determine the distribution of LG north of Mount Bangou in Cameroon. The California Bearing Ratio (CBR), maximum dry density, fines content, and plasticity index are used to assess the geotechnical quality of these materials, with CBR values ranging from 17 to 32%. LG with good geotechnical characteristics covers an area of 50 km2 north of Mount Bangou, with a CBR ≥ 30%, maximum dry density > 1.80, gravel content exceeding 64%, fines content < 30%, and plasticity indices < 30%. LG with moderately good geotechnical characteristics cover an area of 79 km2, with a 25 ≤ CBR < 30% and a gravel content between 53 and 59%. LG with poor geotechnical characteristics cover an area of 61 km2, with CBR values below 25%, gravel content between 38 and 50%, maximum dry density < 1.80, gravel content exceeding 64%, fines content > 30%, and plasticity indices > 25%. Altitude has the greatest influence on the spatial distribution of LG in the landscape. The LG with good geotechnical characteristics were found in areas with high slopes of ≥7° and at altitudes of ≥1700 m. Those with moderately good geotechnical characteristics are located in areas with average slopes of 5° and at average altitudes of 1570 m. LG with poor geotechnical characteristics are observed in areas of low slopes of ≤3° and at altitudes of ≤1600 m. These soils can be used in road layers, especially in foundations and sub-base layers, particularly for very low to moderate traffic. The application of an integrated GIS approach for geotechnical mapping of LG, taking into account genetic and geoenvironmental constraints, is promising. This method can be used to assess larger-scale studies on the spatial distribution of lateritic soils for road construction in the intertropical zone.

Latin American consensus on the treatment of melasma.

Melasma is a chronic, relapsing hyperpigmentation disorder that primarily affects photoexposed areas, occurring most frequently in adult women with darker skin phototypes. The primary factors contributing to its development include sun exposure, sex hormones (e.g., pregnancy), and genetic predisposition. Melasma is highly prevalent in Latin America, where many countries lie in intertropical zones and exhibit significant ethnic diversity because of centuries of intermixing among Native Americans, Europeans, and Sub-Saharan Africans. Nine Latin American experts formulated a DELPHI-based consensus to develop a valuable approach for treating melasma in this diverse population. After establishing an accurate diagnosis, assessing the impact on quality of life, and determining disease severity, the consensus recommends mitigating known triggers and promoting rigorous photoprotection. Active therapy should be tailored based on individual characteristics (e.g., pregnancy status, previous treatments, skin sensitivity). Treatment options include topical depigmenting agents, systemic therapies, and procedural interventions such as laser therapy, microneedling, and chemical peels. Periodic reassessment of the treatment is essential, with strategies adjusted if targeted outcomes are not achieved. Once clinical remission is attained, patients should continue using topical depigmenting agents and maintain strict photoprotection measures to prevent recurrence.

Identification Of Meloidogyne Species Associated With Tomato (Lycopersicon Esculentum L.) In The Bougouni Region (Mali)

Background: The development of market gardening and particularly that of tomatoes is confronted with multiple problems among which there are nematodes of the genus Meloidogyne. The determination of these parasites is important to adopt a control strategy. The objective of this study is to identify Meloidogyne species associated with tomato (Lycopersicon esculentum L.) in the Bougouni region of Mali. Materials and Methods: Root sample collection took place at two sites in Bougouni region. The roots were thinned with bleach 1%. The females were fixed on roots bearing galls in good condition, by the sodium hypochlorite-acid fuchsin method. These females were subsequently dissected and identified using the perineal plates. Results : Microscopic observation of the perineal plates revealed the presence of three types of perineal plates corresponding to M. incognita, M. arenaria and M. javanica with respective rates of 52%, 27% and 21%. Rootknot nematodes are very important in the parasitic nematofauna in Mali, they were found everywhere regardless of the site considered. Conclusion : These results confirm not only the omnipresence of these three genera in the intertropical zone but also the susceptibility of the Roma tomato to Meloidogyne.

Piezometric Modelling of a Hard Rock Aquifer System in An Intertropical Zone: The Case of the Batouri Mining District (South-East Cameroon)

Piezometric Modelling of a Hard Rock Aquifer System in An Intertropical Zone: The Case of the Batouri Mining District (South-East Cameroon)

Geographical and seasonal variations of gravity wave activities in the upper mesosphere measured by space-borne imaging of molecular oxygen nightglow

Geographical and seasonal variations of gravity wave events in the upper mesosphere were investigated using the nightglow imaging data obtained by the Visible and near-Infrared Spectral Imager (VISI) on the Ionosphere, Mesosphere, upper Atmosphere and Plasmasphere (IMAP) onboard the International Space Station (ISS). The nadir-imaging data of the O2(0–0) atmospheric band (762 nm) with the typical emission peak around 95 km altitude was used to investigate small-scale waves (horizontal wavelengths less than ~ 200 km) on a global scale. To detect gravity wave events, the variance of high-pass filtered nightglow images within a local 100 km radius was evaluated, with a threshold set at three times the standard deviation from the average variance of the background level. A data screening algorithm that evaluates the variance of upwelling contamination light emission was also introduced to remove contaminated data. Applying the variance filter and data screening algorithm to a nearly 3-year data set, from November 2012 to August 2015, occurrence maps of wave events for four seasons were derived. The occurrence maps show a higher frequency of wave events in winter high latitudes (> 40° N/S), considerably attributed to gravity wave activity associated with the polar night jet. Hot spots were observed near orographic sources in winter high latitudes, including the eastern part of North America, Europe, and the southern Andes. In the summer hemisphere, hot spots were detected at mid-to-high latitudes such as North America, Europe, and the eastern side of the Eurasian continent, and at equatorial latitudes just above the intertropical convection zone (ITCZ). They are likely gravity waves from deep convection that arise from mid-latitude summertime thunderstorms and the ITCZ, respectively. During the equinox seasons, hot spots were detected near convective sources such as the Amazon Rainforest, Congo Rainforest, and the Indochina peninsula.Graphical

Forty-two-year frequencies of river buffaloes calving in the Terecay ranch, Venezuela

Although buffaloes are polyestrous, they exhibit a distinct seasonal variation in displaying estrus, conception rate, and calving, greatly influenced by physiological, sanitary, nutritional, management, and particularly bioenvironmental factors, such as temperature, humidity, precipitation, evaporation, and daylight duration. Venezuela, a tropical country, is located in the intertropical zone of the northern hemisphere, between the Equator and the Tropic of Cancer, between coordinates 00° 38’ 53” and 12° 11’ 22” LN and 59° 48’ 10” and 73° 25’ 00” LW. The area (Terecay ranch) under study has two well-defined seasons concerning precipitation, with a bimodal behavior, a rainy season (From May to October with an average of 1,441.3 mm/year) and a season with very little or no precipitation (From November to April with an average of 107.4 mm/year). In order to calculate the calving distribution, the records of 13,720 calvings of buffaloes between 1980-2022 corresponding to the Terecay farm located in the Esteros de Camaguan of Guárico State were used. For calculating calving frequency, the PROC FREC procedure of the statistical package SAS version 9.1 was used, and a polynomial regression analysis was performed to evaluate the prediction of future behavior of the calving distribution. The percentage of calving according to the months of the year were: January: 6.96%; February: 4.34%; March: 2.3%; April: 0.95%; May: 0.98%; June: 1.34%; July: 4.39%; August: 11.44%; September: 16.38%; October: 22.32%; November: 15.69% and December 12.91%. The months with the highest average of calving percentages were September (16.38%), October (22.32%), and November (15.69%), and the months with the lowest average percentages were April (0.95%) and May (0.98%). The equation of the polynomial regression analysis was y = -3.0656x4 + 64.363x3 - 360.05x2 + 417.41x + 810.37 with an R² = 0.9571. With this R² value, it can be inferred that the calving behavior will be maintained during these 42 years. Conclusions are that the frequency of calving showed a very marked seasonality between July and January, with 90.09% and 9.91% between February and June. Calving seasonality should be preserved if environmental, nutritional, sanitary, and management conditions are maintained, especially without hormonal interventions.

New geophysical and zircon data support an impact hypothesis for the Velingara structure (Senegal)

On Earth, impact structures are rare in intertropical zones. Here we evaluate the 35–40 km diameter Velingara depression in Senegal as a candidate impact structure. The depression has a topographic relief of only 50 m and is essentially buried under modern sediments. For the first time, potential-field ground observations and a microstructural survey of detrital zircons for shock features were conducted at Velingara. A 15 mGal gravity low in a 10 km diameter central anomaly was found, while significant (100 nT) amplitude magnetic field anomalies were observed in the depression. Forward modeling was used to explain the crustal sources of the anomalies, arguing in favor of the presence of a buried impact structure. An electron backscatter diffraction survey of circa 5,000 detrital zircons from a sample of modern alluvium identified a single granular zircon; orientation data for the grain does not record the former presence of reidite, but does closely resemble grains with highly dispersed neoblast orientations that have only been reported from impact settings. Age determination by LA-ICP-MS indicates the unusual granular zircon recorded an age of ca. 550 Ma. Results of the geophysical data and zircon microstructural survey reported here are consistent with, but do not yet prove, an impact origin hypothesis for the Velingara structure. The difference in amplitude between the diameter of the depression, and that of the gravity anomaly remains puzzling. Several impact scenarios are considered, which include the subsequent evolution via surface processes of a 10-km crater into a larger depression, or a large-scale (d = 40 km) complex impact crater with a peculiar geophysical anomaly limited to its central region.

An early diverging crocodylid from the Middle Miocene of Thailand highlights the role of SE Asia for the radiation of the Crocodyloidea

ABSTRACT The Neogene period witnessed the radiation of modern crocodylian genera, as evidenced from their fossil record in intertropical zones. Despite its recognition as a modern biodiversity hotspot, South East Asia remains undersampled for that age bin. Here, we describe a new crocodylian from northern Thailand, Antecrocodylus chiangmuanensis n. gen. n. sp. from the Middle Miocene lignite seams of Chiang Muan and refer to it other specimens from the nearby lignite seams of Mae Moh. The holotype specimen preserves the posterior half of the skull and mandible. Anatomical observations are aided by medical computed tomography. A phylogenetic analysis places the new taxon in a basal position relative to Crocodylidae. This discovery highlights the underrated fossil record of Neogene crocodyloids in Asia compared to Africa or Australia and allows us to reconsider palaeobiogeographic relationships between supposed endemic clades.

Global distribution modelling of a conspicuous Gondwanian soil protist reveals latitudinal dispersal limitation and range contraction in response to climate warming

AbstractAimThe diversity and distribution of soil microorganisms and their potential for long‐distance dispersal (LDD) are poorly documented, making the threats posed by climate change difficult to assess. If microorganisms do not disperse globally, regional endemism may develop and extinction may occur due to environmental changes. Here, we addressed this question using the testate amoebaApodera vas, a morphologically conspicuous model soil microorganism in microbial biogeography, commonly found in peatlands and forests mainly of former Gondwana. We first documented its distribution. We next assessed whether its distribution could be explained by dispersal (i.e. matching its climatic niche) or vicariance (i.e. palaeogeography), based on the magnitude of potential range expansions or contractions in response to past and on‐going climatic changes. Last, we wanted to assess the likelihood of cryptic diversity and its potential threat from climate and land‐use changes (e.g. due to limited LDD).LocationDocumented records: Southern Hemisphere and intertropical zone; modelling: Global.MethodsWe first built an updated global distribution map ofA. vasusing 401 validated georeferenced records. We next used these data to develop a climatic niche model to predict its past (LGM, i.e. 21 ± 3 ka BP; PMIP3 IPSL‐CM5A‐LR), present and future (IPSL‐CMP6A‐LR predictions for 2071–2100, SSP3 and 5) potential distributions in responses to climate, by relating the species occurrences to climatic and topographic predictors. We then used these predictions to test our hypotheses (dispersal/vicariance, cryptic diversity, future threat from LDD limitation).ResultsOur models show that favourable climatic conditions forA. vascurrently exist in the British Isles, an especially well‐studied region for testate amoebae where this species has never been found. This demonstrates a lack of interhemispheric LDD, congruent with the palaeogeography (vicariance) hypothesis. Longitudinal LDD is, however, confirmed by the presence ofA. vasin isolated and geologically young peri‐Antarctic islands. Potential distribution maps for past, current and future climates show favourable climatic conditions existing on parts of all southern continents, with shifts to higher land from LGM to current in the tropics and a strong range contraction from current to future (global warming IPSL‐CM6A‐LR scenario for 2071–2100, SSP3.70 and SSP5.85) with favourable conditions developing on the Antarctic Peninsula.Main ConclusionsThis study illustrates the value of climate niche models for research on microbial diversity and biogeography, along with exploring the role played by historical factors and dispersal limitation in shaping microbial biogeography. We assess the discrepancy between latitudinal and longitudinal LDD forA. vas, which is possibly due to contrast in wind patterns and/or likelihood of transport by birds. Our models also suggest that climate change may lead to regional extinction of terrestrial microscopic organisms, thus illustrating the pertinence of including microorganisms in biodiversity conservation research and actions.

Analysis Of The Spatial And Temporal Variability Of Rainfall In The Kayanga-Anambé Hydrological Complex (Republic Of Guinea And Senegal)

The high rainfall variability observed especially from the 1970s has intensified the vulnerability of water resources in tropical watersheds. It resulted in the recurrence of extreme hydrological events – combined with the increase in temperature which increases evapotranspiration causing considerable water losses – but also in the "Sahelization" of Sudanian areas resulting in the migration of isohyets towards the south.This article studies recent spatial and temporal changes in rainfall in the Kayanga-Anambé complex, as well as their potential hydrological implications. The methodological approach is based on (i) checking the quality of data and filling gaps using the method of rainfall indices with the Regional Vector Method (RVM); and on (ii) the analysis of spatial and temporal variability of rainfall using PETITT stationarity test and Standardized Precipitation Index (SPI).The evolution of rainfall in the basin is reflected in a fact specific to the intertropical zone, namely the variability of rainfall. This is marked by several sequences: a wet period between 1940 and 1967, followed by a long dry sequence which extends between the beginning of the 70s until the end of the 90s, and finally a slight resumption of the rainfall over the period 1993-2020. However, according to the outputs of global climate models ("Multi-model Ensemble"), the resumption of rainfall in the Kayanga basin will only be effective from 2060. This variability noted in the rains will induce a similar variability in the flows and agricultural production since they are largely dependent on it.

Stoichiometry of carbon, nitrogen and phosphorus is closely linked to trophic modes in orchids

BackgroundMycorrhiza is a ubiquitous form of symbiosis based on the mutual, beneficial exchange of resources between roots of autotrophic (AT) plants and heterotrophic soil fungi throughout a complex network of fungal mycelium. Mycoheterotrophic (MH) and mixotrophic (MX) plants can parasitise this system, gaining all or some (respectively) required nutrients without known reciprocity to the fungus. We applied, for the first time, an ecological stoichiometry framework to test whether trophic mode of plants influences their elemental carbon (C), nitrogen (N), and phosphorus (P) composition and may provide clues about their biology and evolution within the framework of mycorrhizal network functioning.ResultsWe analysed C:N:P stoichiometry of 24 temperate orchid species and P concentration of 135 species from 45 plant families sampled throughout temperate and intertropical zones representing the three trophic modes (AT, MX and MH). Welch’s one-way ANOVA and PERMANOVA were used to compare mean nutrient values and their proportions among trophic modes, phylogeny, and climate zones. Nutrient concentration and stoichiometry significantly differentiate trophic modes in orchids. Mean foliar C:N:P stoichiometry showed a gradual increase of N and P concentration and a decrease of C: nutrients ratio along the trophic gradient AT < MX < MH, with surprisingly high P requirements of MH orchids. Although P concentration in orchids showed the trophy-dependent pattern regardless of climatic zone, P concentration was not a universal indicator of trophic modes, as shown by ericaceous MH and MX plants.ConclusionThe results imply that there are different evolutionary pathways of adaptation to mycoheterotrophic nutrient acquisition, and that the high nutrient requirements of MH orchids compared to MH plants from other families may represent a higher cost to the fungal partner and consequently lead to the high fungal specificity observed in MH orchids.

Fuzzy analytical network techniques for selecting suitable temporary refuge sites in Paez, Colombia

Colombia exhibits a considerable incidence rate of natural disasters because of its location within the intertropical zone, which exposes it to various meteorological and geological phenomena, including the Nevado del Huila volcano. The identification of suitable areas for the installation of temporary shelters is critical for managing these disasters. However, the task of identifying such locations is a complex problem that involves multiple criteria. This study uses a fuzzy systems approach to identify suitable sites for establishing temporary shelters in the Paez municipality during natural disasters, considering the essential criteria determined by experts through pairwise comparisons. The study results indicate that responsiveness is the most significant criterion, followed by area profile. Using these criteria, it identified a specific locality in the Paez municipality as suitable for establishing temporary shelters during natural disasters caused by volcanic phenomena. The findings were compared with those obtained from existing scientific literature and validated by experts in natural disasters. The methodological process described in this study provides a valuable tool for public entities to make informed decisions concerning natural disasters in indigenous territories caused by volcanic phenomena.

Natural Denudation Versus Anthropogenically Accelerated Erosion in Central Brazil: A Confrontation of Time and Space Scales

AbstractLand degradation resulting from increased continental surface erosion is a worldwide and systemic phenomenon due to unsustainable human activities. Already fragile, the intertropical zone is likely to be further affected by climate change like increased aridity, an aggravating factor of soil erosion and land degradation. A major challenge is thus to provide the necessary knowledge to not only deepen our understanding of the Earth's system and its critical thresholds but also to help achieving sustainability. Understanding the factors that control the properties and processes of the critical zone, and especially what will be its responses to ongoing climate and land use changes, requires multidisciplinary efforts to tackle time scales that are compatible with morphogenesis and soil development as well as environmental disturbances of anthropogenic origin. Due to its prominent ecological importance, the Brazilian Cerrado biome is an ideal natural laboratory were to gauge the consequences of recent and intense agricultural activities on continental surface erosion. We focused on the region of Brasília where our approach allows confronting the temporal scales of long‐lived and stable cosmogenic nuclides with that of short‐lived radioactive isotopes, through a comparison of natural and anthropogenically disturbed land surfaces. Our results indicate that long‐term, background denudation rates are lower than 10 mm Kyr−1 whereas recent erosion rates due to human activities may reach rates at least 160 times higher, exceeding by far the sustainability of the soil resource.

Convolutional neural network allows amylose content prediction in yam (Dioscorea alata L.) flour using near infrared spectroscopy.

Yam (Dioscorea alata L.) is the staple food of many populations in the intertropical zone, where it is grown. The lack of phenotyping methods for tuber quality has hindered the adoption of new genotypes from breeding programs. Recently, near-infrared spectroscopy (NIRS) has been used as a reliable tool to characterize the chemical composition of the yam tuber. However, it failed to predict the amylose content, although this trait is strongly involved in the quality of the product. This study used NIRS to predict the amylose content from 186 yam flour samples. Two calibration methods were developed and validated on an independent dataset: partial least squares (PLS) and convolutional neural networks (CNN). To evaluate final model performances, the coefficient of determination (R2), the root mean square error (RMSE), and the ratio of performance to deviation (RPD) were calculated using predictions on an independent validation dataset. The tested models showed contrasting performances (i.e., R2 of 0.72 and 0.89, RMSE of 1.33 and 0.81, RPD of 2.13 and 3.49 respectively, for the PLS and the CNN model). According to the quality standard for NIRS model prediction used in food science, the PLS method proved unsuccessful (RPD < 3 and R2 < 0.8) for predicting amylose content from yam flour but the CNN model proved to be reliable and efficient method. With the application of deep learning methods, this study established the proof of concept that amylose content, a key driver of yam textural quality and acceptance, can be predicted accurately using NIRS as a high throughput phenotyping method. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Assessment of the sensitivity of water resources in the intertropical zone: a bibliographical study with perspectives

Abstract Study of the vulnerability of water resources contributing to consumer health in the inter-tropical zone. The aim of this paper is to present the state of the art on the protection of water resources in the inter-tropical zone in order to identify gabs in knowledge that improve drinking water supply. To achieve this, a documentary search online was carried out to assess the progression of work over time. What emerges from this literature review is that the method for assessing intrinsic and specific vulnerability in bedrock areas is practically non-existent. A discrepancy exists and reflects the difference in a coincidence of the level of vulnerability when several methods of determining vulnerability are used in the same study site. The issue of validation is still problematic, as it lies in the fact that a property that is not precisely defined cannot be unambiguously deduced from the measured quantity. The characterisation of specific pollutants and their propagation in the saturated or groundwater zone are not taken into account. All the different components of the water cycle are not always taken into account during a groundwater vulnerability study, yet each water resource is part of a closely related component of the water cycle.

Fungal feeding preferences and molecular gut content analysis of two abundant oribatid mite species (Acari: Oribatida) under the canopy of Prosopis laevigata (Fabaceae) in a semi-arid land

Prosopis laevigata (mesquite; Fabaceae) forms fertility islands in soils of semi-arid lands where microbial diversity concentrates in response to the accumulation of resources in the soil beneath individual plants, promoting organic matter decomposition and nutrient cycling. This phenomenon provides suitable conditions for the proliferation of key edaphic elements such as fungi and mites. Mite-fungal interactions are central for our understanding of nutrient cycling processes in resource-limited arid food webs; yet, no information is available about fertility islands in semi-arid lands. Thus, we aimed to determine in vitro fungal-based feeding preferences and molecular gut content of the oribatid mite species Zygoribatula cf. floridana and Scheloribates cf. laevigatus, which are abundant under the canopy of P. laevigata in an intertropical semi-arid zone in Central Mexico. Our results on the gut content analysis of these oribatid species resulted in the ITS-based identification of the following fungi: Aspergillus homomorphus, Beauveria bassiana, Filobasidium sp., Mortierella sp., Roussoella sp., Saccharomyces cerevisiae, Sclerotiniaceae sp. and Triparticalcar sp. Furthermore, under laboratory conditions both oribatid mite species exhibited feeding preferences on melanized fungi, such as Cladosporium spp., whereas A. homomorphus and Fusarium penzigi were avoided. Our findings indicated that the analyzed oribatid mite species have similar feeding preferences for melanized fungi, which might suggest resource partitioning and a degree of preference, explaining the coexistence of both oribatid species.

Proposition of correlations for the dynamic parameters of carbonate sands

The offshore industry has been challenged with the necessity to build structures with foundations on carbonate soils, found in extensive areas of the tropical and intertropical zones of the planet. As a better understanding of the behavior of these soils becomes more and more indispensable, this paper presents equations to predict the dynamic behavior of carbonate sands, in which two expressions (G/Gmax versus g and D versus g) were obtained via multiple linear regression using data from resonant column tests carried out on carbonate sands from Cabo Rojo, Puerto Rico (Cataño &amp; Pando, 2010). The proposed equations agreed well with experimental data. The error for the expressions G/Gmax versus g was less than 10%, while the expressions D versus γ trended to underestimate the values for the loose condition (Dr = 24%), presenting an effective confining stress of 50kPa. Furthermore, the proposed equations were compared with predictions exhibited by Javdanian &amp; Jafarian (2018) of G/Gmax versus g and D versus g for carbonate sands, also yielding fairly concordant results.

Austral and Subtropical Gyre Radiolaria – latest Jurassic to Early Cretaceous Leg 123, Site 765, Argo Abyssal Plain revisited: Southern Hemisphere paleobiogeography and global climate change

The aim of this report is to 1) to formally describe Austral and Subtropical Gyre Radiolaria recovered from ODP Hole 123-765C), 2) to compare them with published records of Southern Hemisphere “non-Tethyan” assemblages and 3) to discuss radiolarian paleobiogeography of the Southern Hemisphere and its implications for global climate change during the Jurassic–Cretaceous transition. The Tithonian to Aptian/early Albian radiolarian record recovered from Hole 765C, Cores -62R to -36R in the Argo Abyssal Plain (AAP) is unique in its density of well-preserved samples and in its faunal contents. Radiolaria recovered from claystones yielded the low diversity, ecologically tolerant “Crypto-Archaeo” Assemblage, (chiefly cryptocephalic and cryptothoracic nassellarians and Archeodictyomitra spp.) interpreted herein as originated in the Subtropical Gyre (STG). In contrast, assemblages extracted from radiolarite layers, interpreted as pelagic turbidites derived from the deeper Australian margin, are dominated by Austral taxa. Neotethyan taxa are very rare to absent before the late Hauterivian/Barremian, when they gradually gain in diversity and abundance. Described Austral and STG taxa include 10 families, of which Fusitanellidae n. fam. and Windaliinae n. subfam. are new. Of 18 genera 7 are new (Nodosphaera, Praewindalia, Pachycingula, Archaeotanella, Morchella, Fusitanella, Argofusus) and of 55 species 30 new ones are formally described and 14 new ones are left in open nomenclature. The southern hemisphere Late Jurassic to Early Cretaceous radiolarian biogeography is defined from low- to high latitude: 1. the Neotethyan (NT) and 2. the Central Panthalassan (CP) realms, 3. Eastern Boundary Current (EBC) realm, 4. the Subtropical Gyre (STG) and the Austral (A) circum south-polar realm. Radiolarian biogeography and plate tectonic models support a scenario of palaeoceanographic and global climatic change during the Jurassic–Cretaceous transition related to progressive Pangea break-up with the following consequences: 1. an increased heat transfer to the Southern hemisphere which caused cooling of Neotethyan regions during the Late Tithonian dry event. 2. A northward shift of the southern summer Intertropical Conve nience Zone reduced the Neotethyan monsoon area and allowed the establishment of a southern Neotethyan subtropical gyre documented by the “Crypo-Archaeo” Assemblage. 3. The south-polar West Wind Drift may have forced a circum Antarctic-Australian cold current through the epicontinental rift between India and Antarctica-Australia since the Berriasian (140 my), transporting Austral Radiolaria into the AAP where they accumulated in radiolarite layers.

Kalimantan hydroclimate variability since the last glacial period

Changes in convective activity and hydroclimate over Northeastern Kalimantan are key features to understand glacial to interglacial climate evolution in the center of the West Pacific Warm Pool during the Late Pleistocene to Holocene. We use high-resolution X-ray fluorescence (XRF) scanner-derived elemental ratios in sediment Core SO217-18522 (1º 24.106’ N, 119º 4.701’E, 975 m water depth) recovered from the northern Makassar Strait to reconstruct changes in precipitation-related weathering and erosion over Northeastern Kalimantan over the last 50 kyr. Enhanced seasonality of rainfall and an extended dry season during Heinrich Stadials (HS4 to HS1) and the Younger Dryas (YD) suggest weakening of the tropical convection associated with a southward shift of the tropical rain belt and the annual mean position of the Intertropical Tropical Convection Zone. Increasing sediment discharge and intensification of convective activity occurred during the early to mid-Holocene during an interval of high Northern Hemisphere insolation, elevated atmospheric pCO2 levels and global warming. Our reconstructions in comparison with regional terrestrial and marine records highlight the high spatial variability of Kalimantan hydroclimate on millennial to glacial-interglacial timescales.